1. Field of the Invention
The present invention relates to a method for forming a micro-electromechanical system (MEMS), and more particularly, to a method for forming a cantilever beam type MEMS applied in the field of fiber-optic communication.
2. Description of the Prior Art
Increasingly popular in Internet applications and rapidly developing in transmission capacity,technologies such as cable modem, asymmetric digital subscriber line (ADSL), and dense wavelength-division multiplexing (DWDM) are proposed to solve network jamming problems. Because DWDM has an advantage of transmitting light with multi-wavelengths in a single fiber optic so as to increase the transmission capacity of the fiber optic, DWDM has become one of the most important fiber-optic communication frames.
The DWDM fiber-optic system includes an optical transceiver, a wavelength multiplexer (MUX), a wavelength demultiplexer (D-MUX), an erbium-doped fiber amplifier (EDFA), an add-drop multiplexer, a dispersion compensation device, a filter, an optical switching router, other optical communication devices, processing circuits, and optical mechanisms. In the field of fiber-optic communication, techniques for forming the DWDM include an optical filter type, a fiber-optic grating type, a fiber-optic coupler type, and a waveguide type. The optical filter utilizes prisms or thin film filters (TFFs), the fiber-optic grating utilizes various kinds of optical gratings, such as a fiber bragg grating (FBG) or an arrayed waveguide grating (AWG), and the fiber-optic coupler utilizes various kinds of interferometers, such as a fabry-perot interferometer or a mach-zehnder, to filter wavelengths and splitting beams of multi-channel in optics.
In actual applications, the low cost fiber-optic coupler only transfers 8 wavelengths and is suitable for local network applications, the fiber-optic grating and the waveguide can transfer 64 wavelengths and above and is suitable for a long-distance communication network, and the optical filter can transfer about within 32 wavelengths. In addition, the TFF has an advantage of thermal stability, but due to standards specifying close confinementof optics, the TFF has low yield, high cost, and can not replace the original filters entirely. However, since the AWG technique utilizes a planar optical waveguide method to couple a demand wavelength, and since the manufacturing processes of the AWG are similar to the ordinary semiconductor processes, the original filters can be replaced by the AWG technique, and the AWG can become enter the main-stream market with the increasing demand of high channels.
This kind of micro-electromechanical system (MEMS) incorporates characteristics in optics, mechanics, and electronics, and is manufactured by ordinary semiconductor processes. Data is transferred and always retained in a beam type during the transmissionprocess in MEMS. That is to say, the data does not have to be transformed to an electrical type, and transformed into a beam-to-beam type. And since adjustable microstructures can be formed by using the micro-electromechanical techniques, the MEMS has received much attention from the fields of fiber-optic communication and wireless radio frequency (RF) communication. Therefore, the MEMS techniques have been applied to form the optical communication devices recently, and the traditional photoelectric switching devices are replaced gradually by the MEMS in an optic-electronic-optic (OEO) transform procedure of the DWDM system.
It is therefore a primary objective of the claimed invention to provide a method for forming a cantilever beam type micro-electromechanical system (MEMS).
It is another object of the claimed invention to provide a simplified method for forming a cantilever beam type MEMS to reduce costs.
It is another object of the claimed invention to provide a method for forming a MEMS for being an photoelectric switching device to filter wavelengths or split beams of multi-channel in a field of fiber-optic communication.
According to the preferred embodiment of the claimed invention, the cantilever beam type MEMS is formed on a semiconductor substrate including a heavily doped layer and a first dielectric layer formed on the semiconductor substrate. First, at least two first conductors connected to a surface of the heavily doped layer are formed in the first dielectric layer, and a second dielectric layer not connected to the surface of the heavily doped layer is formed in the first dielectric layer between the first conductors. Then, a patterned sacrificial layer and a third dielectric layer are formed on the substrate, and at least two second conductors and a fourth dielectric layer are formed in the third dielectric layer. Further, a plurality of openings are formed in the fourth dielectric layer, and a cap layer is formed on the substrate. Finally, the patterned sacrificial layer is removed by an isotropic etching process.
In the claimed invention, the cantilever beam type MEMS incorporates the fiber-optic grating type DWDM to filter wavelengths and split beams of multi-channel in the field of fiber-optic communication. And because the MEMS are formed by ordinary semiconductor equipment and ordinary semiconductor processes, the processes are simplified, products can be manufactured on a large scale, and costs can be reduced. In addition, the MEMS has a small size so that the MEMS has a shorter reaction time and needs fewer power to operate it.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.